Geochemistry and petrogenesis of basement grey granitoid gneisses from the Chhotanagpur Gneissic Complex, eastern India: Implications for the Mesoproterozoic continental arc magmatism

Abstract

This study investigates the basement migmatitic Grey Granitoid Gneisses (GGG) along the southern margin of the Chhotanagpur Gneissic Complex (CGC) in the Eastern Indian Shield through detailed petrography, mineral chemistry, whole-rock geochemistry, LA–ICP–MS U–Pb zircon geochronology, Hf isotopic analysis, and petrogenetic–tectonic interpretation. The GGG consists of medium-grained, granoblastic mesosomes with compositions spanning tonalite, trondhjemite, granodiorite, and granite. These rocks exhibit calc-alkaline, I-type affinities are metaluminous to weakly peraluminous, and range from magnesian to ferroan. Zircon grains are stocky to moderately elongate, mostly subrounded to rounded, and display oscillatory zoning, consistent with magmatic crystallization. Both whole-rock and zircon REE patterns show moderate fractionation with negative Eu anomalies. Primitive mantle–normalized spider diagrams reveal enrichment in Rb, K, Ba, Th, and U, and pronounced depletion in Nb, Ta, Sr, P, and Ti—signatures characteristic of arc-related granitoids. Low Nb/U (4.07–7.3) and Ce/Pb (0.52–4.1) ratios, together with high Th/U ratios (9.48–11.14), further indicate a predominantly crustal source. U–Pb zircon dating constrains GGG magmatism to 1397 ± 18 Ma (MSWD = 1.9). Zircon Lu–Hf isotopic compositions [εHf(t) = + 2.52 to − 6.86; T_DM2 = 1.7–2.4 Ga] suggest derivation from juvenile amphibolitic lower crust variably hybridized with older crustal components. The presence of inherited 1616 Ma zircons, along with enclaves of amphibolite and migmatite, attests to direct remelting of older crust. Petrogenetic modeling indicates that the GGG mesosomes formed through ~ 20% partial melting of high-K metabasalts (amphibolites). Collectively, these results suggest that the 1616 Ma amphibolitic crust in the study area originated within a regional Paleoproterozoic continental arc–back-arc system along the Satpura Orogenic Belt, and subsequently served as a fertile source for Mesoproterozoic hybrid magmatism.